Energy absorbing bumper mount

ABSTRACT

A collision bumper is supported on a vehicle chassis frame for relative longitudinal bodily movement by a pin and slot connection with relative bodily movement being normally rigidly resisted by substantial mechanical friction between the bumper and the chassis frame. A metal strap formed with a single convolution is connected at one end to the bumper and at the other end to the chassis frame. When an impact on the bumper results in a force on the latter of extraordinary magnitude, the frictional resistance to relative bodily movement is overcome and the bumper is forced rearwardly against the friction to effect primary energy absorption. Simultaneously, tensile forces exerted by the bumper on the strap initiate localized plastic deformation thereof to effect secondary energy absorption.

United States Patent Diener [54] ENERGY ABSORBING BUMPER MOUNT [72]Inventor: James H. Diener, Lansing, Mich.

[73] Assignee: General Motors Corporation,

Detroit, Mich. Y [22] Filed: Feb. 25, 1971 [2]] Appl. No.: 118,703

[52] US. Cl. .293/89, l88/l C, 293/99' [5 l] Int. Cl. ..B60r 19/04 [58]Field of Search ..293/l, DIG. 3, 60, 70, 86,

293/89, 99, lOl; 188/] B, l C; 213/1 A [:56] References Cited UNITEDSTATES PATENTS 3,006,484 10/1961 Pringiers ..213/22o 3,447,833 6/1969Rice ..297/386 3,519,301 7/ i970 1 Somnitz ..293/1 1 51 Oct. 10,1972

Primary Examiner-Arthur L. La Point Assistant Examiner-Robert SaiferAttorney-W. E. Finken and D. L. Ellis 1 [57 ABSTRACT A collision bumperis supported on a vehicle chassis frame for relative longitudinal bodilymovement by a pin and slot connection with relative bodily movementbeing normally rigidly resisted by substantial mechanical frictionbetween the bumper and the chassis frame.

A metalstrap formed with a single convolution is connected at one end tothe bumper and at the other end tothe chassis frame. When an impact onthe bumper results in a force on the latter'of extraordinary mag-.nitude, the frictional resistance to relative bodily movement isovercome and the bumper is forced rearwardly against the friction toeffect primary energy absorption. Simultaneously, tensile forces exertedby the bumper on the strap initiate localized plastic deformationthereof to effect secondary energy absorption.

3 Clairrs, 4 Drawing Figures PATENTED T 3.697. 108

,wzzu Y ATTORNEY ENERGY ABSORBING BUMPER MOUNT This invention relatesgenerally to vehicle collision bumpers and in particular to energyabsorbing mounts therefor.

The primary feature of this invention is that it provides an improvedvehicle collision bumper mount of the mechanical friction energyabsorbing type wherein bodily movement of the bumper relative to thevehicle body in response to the impact of forces of extraordinarymagnitude on the bumper takes place against uniform resistance ofmechanical friction for purposes of effecting primary absorption of theenergy imparted to the bumper by the impact. Another feature of thisinvention resides in the provision in the bumper mount of secondaryenergy absorbing means including a connecting member mounted between thevehicle body and the bumper such that relative bodily movement of thelatter is necessarily accompanied by permanent distortion of theconnecting member with consequent additional-or secondary energyabsorption. Yet another feature of this invention resides in theprovision in the secondary energy absorbing means of a strap typeconnecting member having convolutions intermediate the ends thereofdefining a predetermined number of stress concentrations, the strapbeing attached at respective opposite ends to the vehicle body and tothe bumper so that relative bodily movement of the latter effectsplastic deformation of the strap at the stress concentrations with theamount and rate of energy absorbed thereby being dependent upon theconfiguration of the convolutions and the physical characteristics ofthe strap.

These and other features of this invention will be readily apparent fromthe following specification and from the drawings wherein:

FIG. 1 is a perspective view of an automobile chassis frame having abumper structure supported thereon by a pair of energy absorbing mountsaccording to this invention;

FIG. 2 is a view taken generally along the plane indicated by lines 2-2in FIG. 1;

FIG. 3 is an enlarged sectional view taken generally along the planeindicated by lines 3-3 in FIG. 2; and

FIG. 4 is an exploded perspective view of an energy absorbingmount'according to this invention.

Referring now to FIG. 1 of the drawings, there is shown in simplifiedform an automobile chassis frame designated generally including a pairof longitudinally extending box section frame rails 12 and 14, the framerails being interconnected at the forward end of the chassis frame by arigid cross member 16. A collision bumper structure designated generally18 including a bumper bar 20 having a pair of spaced rigid struts 22 and24 projecting therefrom is supported on the chassis frame by a pair ofenergy absorbing mounts according to this invention and designatedgenerally 26 and 28. It will, of course, be understood that the energyabsorbing mounts according to this invention while being shown incombination with a separate chassis frame are equally well adapted foremployment in unibody constructions. I

Except for reversal of orientation, the energy absorbing mounts 26 and28 are structurally identical and the following discussion is,accordingly, a description of only the mount 28, it being understoodthat the mounts function identically. As seen best in FIGS. 2, 3 and 4,

the strut 24 projecting from the bumper bar 20 has therein a pair oflongitudinally spaced slots 30 and 32, an enlarged slot 34 and anaperture 36 with counterbore 38. Each of the slots 30 and 32 slidablyreceives the shank of a respective one of a pair of threaded studs 40and 42 rigidly secured by conventional means to frame rail 14 at theforward end thereof. The spaced studs 40 and 42 function, through strut24, to support the bumper structure 18 on the chassis frame incantilever fashion and for limited longitudinal bodily movement relativeto the latter.

The strut 24 is retained on the chassis frame and restrained againstlateral movement relative thereto by a pair of large flat washers 44 anda pair of nuts 46, a respective one of each of the flat washers and nutsbeing received on each of the studs 40 and 42. In addition to retainingthe strut on the chassis frame the nuts and flat washers function aspart of the primary energy absorbing means of the mount 28. Moreparticularly, with strut 24 captured between the outboard side of framerail 14 and the flat washers, tightening of the nuts 46 generatessubstantial mechanical friction between opposite sides of the strut 24and the frame rail and flat washers, the magnitude of the mechanicalfriction, of course, being directly proportional to the torque to whichthe nuts 46 are subjected. The mechanical friction thus generatedresists relative bodily movement of the strut, and hence of the bumperstructure, in either direction.

Normally, the bumper structure is supported on the chassis frame 10 in afully extended position, FIGS. 1 and 2, with the studs 40 and 42situated at the rearward ends of the corresponding ones of the slots 30and 32. In addition, the nuts 46 are tightened or torqued down on thestuds 40 and 42 an amount sufficient to generate enough mechanicalfriction between the strut and the frame rail and flat washers tosuccessfully resist relative bodily movement of the bumper structurewhen the bumper bar is subjected to impact forces below a predeterminedmagnitude. The value of the predetermined force magnitude is somewhathigher than the magnitude of the most severe force to which the bumperbar might be expected to be subjected during everyday vehicle operationso that the bumper structure is, in effect, normally rigidly supportedon the chassis frame.

In an unusual situation, however, as when a collision results in impactforces on the bumper bar of extraordinarily high magnitude, thepredetermined force magnitude is very rapidly exceeded. When thepredetermined magnitude is exceeded, the mechanical frictionalresistance to relative bodily movement is overcome and the strut andentire bumper structure are forced rearwardly relative to the chassisframe against the uniform resistance of the mechanical friction. As thebumper structure so moves, the energy imparted thereto by the abnormallysevere impact force is absorbed by the mount 28 in a primary mode anddissipated at a relatively uniform rate as heat generated by friction.

Since the magnitude of the extraordinary impact forces are widelyvariable and may quite substantially exceed the magnitude required toinitiate primary energy absorption, the mount 28 incorporates secondaryenergy absorbing means which function during primary energy absorptionto effect additional or secondary absorption of the energy of impact. Asseen best in FIGS. 2, 3 and 4, the secondary means includes a connectingmember in the form of a metal strap 48 formed with a single convolution50 and having a pair of clearance apertures 52 and 54 therein. As seenbest in FIG. 3, a bolt 56 is received in aperture 36 in the strut withthe head portion thereof seating in counterbore 38. The shank of bolt 56is received within aperture 52 in the strap 48 and the latter isretained by a nut 58 threadedly received on bolt 56, nut 58 thusfunctioning to rigidly secure one end of strap 48 to the rearward end ofstrut 24.

Referring now to FIGS. 2 and 4, a cylindrical spacer member 60 isclosely received on the shank of a third threaded stud 62 rigidlyaffixed to and projecting outboard from frame rail 24. The diameter ofthe spacer member is less than the width of the enlarged slot 34 in thestrut so that when the spacer member is slid down on stud 62 into flushengagement with the outboard surface of frame rail 24, relative bodilymovement of the strut is unimpaired. Aperture 54 in strap 48 receivesthe shank of the third stud 62 outboard of the spacer member 60 and boththe strap and spacer member are retained on the stud 62 by a nut 64threadedly received on the latter, nut 64 thus rigidly attaching theforward end of the strap 48 to the chassis frame.

As seen best in FIG. 2, the position of third stud 62 on the frame rail24 is predetermined to insure that when the bumper structure 18 is inits normal fully extended position the stud and attached spacer member60 are situated adjacent the rearward end of enlarged slot 34.Similarly, in the extended position of the bumper structure the strap 48assumes an initial undistorted and unstressed position.

In a typical energy absorbing cycle of operation of the mount 28,primary energy absorption effected through mechanical friction, asdescribed, is simultaneously accompanied by additional or secondaryenergy absorption effected through forcible distortion of the strap 48.More particularly, so long as the mechanical frictional resistance torelative bodily movement of the strut maintains the latter rigid, noforces act on the strap. At the instant the predetermined forcemagnitude necessary to overcome the mechanical friction is exceeded andbefore relative bodily movement of the strut commences, the strap issubjected by the strut to rapidly increasing tensile forces which forcestend to resist relative bodily movement of the strut. The strap,however, is formed with predetermined areas of stress concentration, asat the base of convolution 50, so that when the tensile forces reach apredetermined value the stress at the concentrations exceeds the elasticlimit of the material whereupon localized plastic deformation withconsequent secondary energy absorption commences. As the strap distortsthe strut moves rearwardly relative to the frame rail against theuniform frictional resistance of the primary energy absorbing means andagainst the tensile force which must be maintained on the strap toeffect forcible distortion thereof. Accordingly the net energyabsorption effected is the sum of that effected by the primary andsecondary means, the former being uniform and the latter being variablein accordance with configuration and physical characteristics of thestrap.

It will be apparent to those skilled in the art that while the strap 48with single convolution 50 shown effects secondary energy absorption ata uniform rate, other configurations are possible by which the resistingforce exerted on the strut, and hence the secondary energy absorption,vary in proportion to the displacement of the strut relative to thevehicle body. It will be further apparent that after the cessation ofenergy absorbing operation the mount 28 can be easily and quickly resetfor another cycle by removing the distorted strap 48, loosening nuts 46to permit manual return of the bumper structure to the extendedposition, reattaching a new undistorted strap between the strut and theframe rail, and retightening nuts 46. Finally, the terms primary energyabsorption and secondary energy absorption as used herein are intendedto denote only the two modes of energy absorption described and are notintended to reflect on the relative amounts of energy absorbed.Accordingly, either friction or plastic deformation may account for 50percent more of the total amount of energy absorbed.

Having thus described the invention, what is claimed rs:

1. In a vehicle, the combination comprising, a collision bumperstructure, a primary energy absorbing means operative to normallyrigidly support said bumper structure on said vehicle and to effectabsorption of energy imparted to said bumper structure by extraordinaryimpacts thereon by permitting bodily movement of said bumper structurerelative to said vehicle against substantial mechanical frictionalresistance, and a secondary energy absorbing means operativesimultaneously with said primary means to effect additional absorptionof the energy imparted to said bumper structure, said secondary meansincluding a plastically deformable connecting member, means rigidlyattaching a first portion of said connecting member to said bumperstructure, and means rigidly attaching a second portion of saidconnecting member to said vehicle so that during relative bodilymovement of said bumper structure forces applied to said connectingmember by said bumper structure cause energy absorbing plasticdeformation of said connecting member.

2. In a vehicle, the combination comprising, a collision bumperstructure, a primary energy absorbing means operative to normallyrigidly support said bumper structure on said vehicle and to effectabsorption of energy imparted to said bumper structure by extraordinaryimpacts thereon by permitting bodily movement of said bumper structurerelative to said vehicle against substantial mechanical frictionalresistance, and a secondary energy absorbing means operativesimultaneously with said primary means to effect additional absorptionof the energy imparted to said bumper structure, said secondary meansincluding a strap having a plurality of convolutions therein definingstress concentrations thereon, means rigidly attaching one end of saidstrap to said bumper structure, and means rigidly attaching the otherend of said strap to said vehicle so that during relative bodilymovement of said bumper structure forces applied to said strap by saidbumper structure cause stresses at said stress concentrations whichexceed the elastic limit of the material of said strap and therebyeffect localized energy absorbing plastic deformation of the latter.

3. In a vehicle, the combination comprising, a collision bumperstructure including a rigid strut having an enlarged aperture therein,means supporting said rigid strut on said vehicle for longitudinalbodily movement relative to the latter, means on said vehicle and onsaid strut operative to develop substantial mechanical fn'ctiontherebetween, said mechanical friction normally maintaining said strutand said bumper structure rigid with respect to said vehicle andproviding uniform resistance to relative bodily movement of said bumperstructure and said strut to effect absorption of energy imparted to saidbumper structure when the latter is subjected to forces of magnitudesufficient to overcome said frictional resistance and bodily move saidbumper structure and said strut relative to said vehicle,

a metal strap having a convoluted portion intermediate the ends thereofdefining a plurality of areas of stress concentration in the strap,means rigidly attaching one end of said strap to said rigid strut, andmeans projecting through said enlarged aperture in said rigid strutrigidly attaching the other end of said strap to said vehicle so thatbodily movement of said strut relative to said vehicle subjects saidstrap to tensile forces, said tensile forces upon achieving apredetermined magnitude being operative to generate stresses in saidstrap at said areas of stress concentration which exceed the elasticlimit of the material of said strap and thereby effect localized energyabsorbing plastic deformation of the latter.

1. In a vehicle, the combination comprising, a collision bumperstructure, a primary energy absorbing means operative to normallyrigidly support said bumper structure on said vehicle and to effectabsorption of energy imparted to said bumper structure by extraordinaryimpacts thereon by permitting bodily movement of said bumper structurerelative to said vehicle against substantial mechanical frictionalresistance, and a secondary energy absorbing means operativesimultaneously with said primary means to effect additional absorptionof the energy imparted to said bumper structure, said secondary meansincluding a plastically deformable connecting member, means rigidlyattaching a first portion of said connecting member to said bumperstructure, and means rigidly attaching a second portion of saidconnecting member to said vehicle so that during relative bodilymovement of said bumper structure forces applied to said connectingmember by said bumper structure cause energy absorbing plasticdeformation of said connecting member.
 2. In a vehicle, the combinationcomprising, a collision bumper structure, a primary energy absorbingmeans operative to normally rigidly support said bumper structure onsaid vehicle and to effect absorption of energy imparted to said bumperstructure by extraordinary impacts thereon by permitting bodily movementof said bumper structure relative to said vehicle against substantialmechanical frictional resistance, and a secondary energy absorbing meansoperative simultaneously with said primary means to effect additionalabsorption of the energy imparted to said bumper structure, saidsecondary means including a strap having a plurality of convolutionstherein defining stress concentrations thereon, means rigidly attachingone end of said strap to said bumper structure, and means rigidlyattaching the other end of said strap to said vehicle so that duringrelative bodily movement of said bumper structure forces applied to saidstrap by said bumper structure cause stresses at said stressconcentrations which exceed the elastic limit of the material of saidstrap and thereby effect localized energy absorbing plastic deformationof the latter.
 3. In a vehicle, the combination comprising, a collisionbumper structure including a rigid strut having an enlarged aperturetherein, means supporting said rigid strut on said vehicle forlongitudinal bodily movement relative to the latter, means on saidvehicle and on said strut operative to develop substantial mechanicalfriction therebetween, said mechanical friction normally maintainingsaid strut and said bumper structure rigid with respect to said vehicleand providing uniform resistance to relative bodily movement of saidbumper structure and said strut to effect absorption of energy impartedto said bumper structure when the latter is subjected to forces ofmagnitude sufficient to overcome said frictional resistance and bodilymove said bumper structure and said strut relative to said vehicle, ametal strap having a convoluted portion intermediate the ends thereofdefining a plurality of areas of stress concentration in the strap,means rigidly attaching one end of said strap to said rigid strut, andmeans projecting through said enlarged aperture in said rigid strutrigidly attaching the other end of said strap to said vehicle so thatbodily movement of said strut relative to said vehicle subjects saidstrap to tensile forces, said tensile forces upon achieving apredetermined magnitude being operative to generate Stresses in saidstrap at said areas of stress concentration which exceed the elasticlimit of the material of said strap and thereby effect localized energyabsorbing plastic deformation of the latter.